The present invention comprises an improved, comparatively low-cost liquid metering device of the general type contemplated in our prior U.S. Pat. No. 3,714,823 issued Feb. 6, 1973, for "Fuel Consumption Meter" and U.S. Pat. No. 3,937,083 issued Feb. 10, 1976, for "Temperature-Compensating Liquid Meter". These known types of meters comprise a measuring chamber having a pair of liquid-level sensors therein which are disposed in vertically spaced relation to one another, and the metering device includes control means responsive to the absence of liquid in the measuring chamber at a first level determined by the lower one of the sensors for feeding liquid to be measured from a supply of said liquid to the measuring chamber, the control means being subsequently responsive to the presence of liquid in the measuring chamber at a second level determined by the upper one of the sensors for terminating the feeding of liquid into the measuring chamber and for substantially simultaneously withdrawing liquid from the measuring chamber until the level of said liquid in the measuring chamber falls to the said first level whereupon the withdrawal of liquid from the measuring chamber is terminated and liquid to be measured is again fed from the liquid supplied to the measuring chamber. By such operation, fixed increments of liquid to be measured, each of which increments is volumetrically dependent upon the vertical spacing between the sensors, are repetitively fed to and thereafter withdrawn from the measuring chamber; and a counter arrangement can be provided to count the number of increments of liquid which are withdrawn from the measuring chamber thereby to provide a digital measurement of fuel flow or, when the device is employed in a vehicle, to provide a digital measure of fuel consumption by the vehicle.
The arrangements which are contemplated in our prior patents are vented to atmospheric pressure wherefore, when used to measure fuel consumption in a vehicle, they have required a pump additional to the pre-existing fuel pump in the vehicle and, moreover, have been incapable of being located within the fuel tank of the vehicle itself. The present invention provides significant improvements in this respect since it employs a sealed housing arrangement which is adapted to be mounted directly in the fuel supply tank of a vehicle, thereby to secure the meter from leakage and to reduce the possibility of vandalism, and which employs components which are arranged to give a highly accurate digital or analog measurement of fuel or liquid flow by means of a metering device which is far lower in cost than metering devices suggested heretofore.
For purposes of the subsequent description, it will be assumed that the metering device of the present invention is used in conjunction with a motor vehicle; however the device of the present invention can measure any slow flowing liquid and can therefore be utilized as a general purpose flow meter. Moreover, the device of the present invention will be described in reference to an in-tank installation of the meter, which constitutes a preferred embodiment of the invention, but the sealed meter of the present invention can be mounted externally of the tank or other supply of liquid or fuel being measured.